1. They randomly lick things or people. There is no explanation for this. Science has worked hard to discover the reason. But whether it's to replaced mineral deficiencies or they are genuinely curious, it's just not right.
2. They can watch the same show over and over. It's cause the government is brainwashing them.
3. They make up words so you can't understand them.
4. They delight in seeing others get hurt and often will do things to hurt themselves.
5. No matter how much they eat at a meal, they are always hungry 5 minutes later.
6. The point or stare at everything.
7. They eat buggers or scabs.
8. They sometimes eat so much they get sick.
9. They have imaginary friends. (This is kind of cute. But can be annoying when you have to wait for the 'friend')
10. They wipe things on their pants instead of using a napkin or washing their hands.
There's no explanation for this, it's all just weird. So embrace the weirdness and have a blast laughing at your kids odd ways.